Effect Of Annual Returning Of Rice And Wheat Straws On Rice Yield And Soil Properties

As a main way to reuse straw resources in the farmland,straw-returning to the soil can effectively alleviate adverse effects of direct straw-burning on the soil and environment.Although there are previous studies on this aspect,few studies investigate the effect of annual returning of rice and wheat straws on rice yield and soil properties.In this study,Japonica inbred Huaidao 5 and Japonica/Indica hybrid Yongyou 2640 were used were used as materials,and field experiments were conducted with four treatments:(A)no straw-returning(straw was not returned to the soil,control),(B)wheat straw-returning(wheat straw was returned to the soil after wheat harvesting and before the rice season),(C)rice straw-returning(rice straw was returned to the soil after rice harvesting and before the wheat season,and(D)annual returning of rice and wheat straws,both B and C.the effect of the straw-returning treatments on grain yield of rice,above ground morphological and physiological traits,root traits,soil properties,and greenhouse gas emissions were investigated.The objective of this study was to elucidate the characteristics of yield formation,the changes in soil properties and greenhouse gas emissions under the condition of annual returning of rice and wheat straws The main results are as follows.1.Effect of annual returning of rice and wheat straws on the grain yieldThe grain yield of Huaidao 5 and Yongyou 2640 was significantly increased by the straw-returning treatments.Compared with that under the control(no straw-returning),the grain yield of Huaidao 5 was 9.47 t hm-2,9.20 t hm-2 and 9.60 t hm-2,respectively,under the wheat straw-returning,rice straw-returning,and annual returning of rice and wheat straws,which was increased by 10.29%,7.08%and 11.85%,respectively,the grain yield of Yongyou 2640 was 11.74 t hm-2,11.59 t hm-2,and 12.24 t hm-2,respectively,under the wheat straw-returning,rice straw-returning,and annual returning of rice and wheat straws,which was increased by 7.96%,6.54%and 12.54%,respectively,compared with the control.The increased grain yield was mainly attributed to the significant increase in total spikelet number.Compared with the control,the total spikelet number of Huaidao 5 was increased by 10.95%,7.78%,and 12.97%,and that of Yongyou 2640 was increased by 5.73%,4.96%,and 10.88%,respectively,under the wheat straw-returning,rice straw-returning,and annual returning of rice and wheat straws treatments.The results indicate that the yield-increasing effect is great under the annual returning of rice and wheat straws treatment than under either the wheat straw-returning or the rice straw-returning treatment,and is greater under the wheat straw-returning than under the rice straw-returning treatment.2.Mechanism underlying the increase in grain yield under straw-returning treatmentsStraw-returning to the soil significantly optimized soil physical and chemical properties,such as reducing soil bulk density,increasing soil porosity,soil respiration rate,and soil nutrient content,enhancing the activities of carbon and nitrogen metabolic enzymes in the soil,and improving soil carbon and nitrogen cycle process The straw-returning treatments improved root morphology,increased root activity,promoted the absorption of nitrogen,phosphorus and potassium,and significantly enhanced the photosynthetic ability,the assimilate accumulation and transport during grain filling,and consequently,significantly increased the grain yield of rice.3.Effect of straw-returning on the greenhouse gas emissions from the paddy fieldCompared with the control,all straw-returning treatments significantly increased greenhouse gas emissions from the paddy field,especially CH4 emission,leading to increases in the global warming potential(GWP)and greenhouse gas emission intensity(GHGI)during rice season,with the most increase for the annual returning of rice and wheat straws treatment.However,there was significant difference in GHGI between the two rice varieties.The GHGI of Yongyou 2640 was significantly lower than that of Huaidao 5.Therefore,the environmental cost of per unit grain yield of Yongyou 2640 was lower than that of Huaidao 5,which was due mainly to a higher grain yield for Yongyou 2640 than for Huaidao 5.In conclusion,straw-returning,especially the annual returning of rice and wheat straws,to the soil could significantly increase grain yield of rice and improve paddy soil properties.However,straw-returning treatments could increase greenhouse gas emissions from the paddy field.Using a high-yielding rice variety could produce more grain yield at a lower environmental cost.